Electroless nickel solution control



United States Patent ELECTROLESS NICKEL'SOLUTION CONTROL Robert A. Spanlding, Huntington Woods, Mieh., assignor -t0 General Motors-Corporation, Detroit, Mich., a corporation of Delaware No Drawing. Application December 3, 1953, Serial No. 396,081

12 Claims. (Cl. 117-130) This invention relates .to improvements in the deposition of nickel from chemical reduction plating solutions and more particularly to the control and maintenance of such solutions.

It is known that nickel and certain other metals can be deposited on a metallic article by immersion of the article in an aqueous solution of a salt of the metal to be deposited and a reducing agent such as sodium hypophosphite or potassium hypophosphite. Plating of this type, generally termed electroless plating, is conducted in 'an acid or alkaline solution maintained at a temperature of about 90 C. or higher. In many instances, certain catalytic metals are employed to initiate the oxidation-reduction plating reaction. Nickel has heretofore been deposited from such an aqueous solution of nickel chloride and sodium hypophosphite or potassium hypophosphite.

However, during the oxidation-reduction plating proc- .ess certain undesirable reaction products are formed which heretofore have considerably shortened the effective life of the plating solution, thereby limiting the use of electroless plating in large scale applications. In addition to substantially pure nickel the principal products of the plating reaction are chlorides, soluble phosphites and an acid, the particular acid depending on the source of nickel employed. Since optimum nickel deposits gen erally are obtained at a pH within the range of about 4 to 6, it is necessary to periodically adjust the pH which would otherwise be reduced by the gradual accumulation in the bath of by-product acid. However, from a practical standpoint, the most troublesome 'by-products are the phosphites which reduce the stability of the bath and cause a rough and/or pitted deposit of nickel.

I have now discovered that the aforementioned difiiculties can be avoided by treating the plating solution with an ion exchange material which has adsorbed hypophosphorous acid or a soluble hypophosphite. As a result of such a treatment, whether continuous or intermittent, the plating solution phosphite content is exchanged for hypophosphite, thereby eliminating the principal undesirable by-product and simultaneously adding fresh hypophosphite reducing agent to the plating solution.

The anion exchange material to be used in any particular application will depend on a number of factors. In general, however, I prefer to employ an ion exchange material which is weakly basic so as to avoid adsorption of weakly acidic bath constituents. Depending on the particular application, suitable ion exchange materials include inorganic substances such as dolomite (calciummagnesium-carbonate); synthetic inorganic materials such as heavy metal silicates; as well as various organic ion exchange resins including phenolic or phenolic derivative type resins prepared by the polymerization of an aromatic amine, such as aniline or metaphenylene diamine and formaldehyde; or by the reaction of a polyamine, phenol and formaldehyde. Other satisfactory anion exchange resins include those formed by nitration and reduction of copolymers of styrene, divinylbenzene and/or other unsaturated compounds. Resins of the anion exchange type generally are characterized by reactive 'hydroxy groupings or amine type groupings as follows:

where R is an aromatic or alkyl substituent group.

Examples of commercially available anion exchange resins are the following:

Wofatit M (I. G. Farben) Duolite A-2 (Chemical Process) Duolite A3 (Chemical Process) De Acidite (Permutit Co.)

Permutit W (Permutit Co.) Amberlite IR4B (Rohm & Haas) Amberlite lRl5 (Rohm & Haas) Ionac A-300 (American Cyanamid Co.)

In the practice of the present invention, an ion exchange resin, here indicated as R(OH)2, is treated with a solution of a soluble 'hypo'phosphite or hypophosphorous acid as follows:

or (2) R (OH)2+ZH3PO2 R(I-IzPO2)2+-ZH2O Used plating solution, contaminated with phosphite, 'is then passed through the resin treated according to Reaction 1 or 2: (3) R(HzPO2)2+NaH2PO3 (used plating solution RHPO3+ (HsPOz-i-Nal-lzPOz) plating solution In many instances, instead of adding acid to the solution as is indicated by Reaction 3, it is desirable to :activate or regenerate only a portion of the ion exchange resin. Hence, in a preferred bath treatment the exchange reaction is as follows:

(4) R OH) 2IR(H2PO2 2+NaH2PO3 (used plating solution) +2R(HPO3) +2NaI-I2POz (plating solution) The ion exchange resin, now contaminated by phosphite, may be stripped with caustic soda generally as follows:

Instead of using caustic soda, it will be understood, of course, that the ion exchange material may be stripped or regenerated with sodium carbonate or ammonium hydroxide, as well as other basic materials.

Since electroless nickel plating baths frequently contain ingredients other than the source of nickel and reducing agents, it is preferred to select an ion exchange resin which will not adsorb desirable bath constituents, such for example, as glycollic acid. in regenerating the ion exchange resin as indicated in Reaction 3, I have found that it is desirable to employ hypophosphorous acid in an amount equivalent to about /5 weight of sodium' phosphite which is to be removed from the plating solution. I V

The following are illustrative of the practice of the present invention:

Example 1 A nickel reduction plating solution, having a pH of 4.82 and containing 110.8 g./l. of Nazi-IP03 and 5.7 g./l. of NaHzPOz, was treated with 14.5 g./l. of hypophosphorous acid (in terms of NaHzPOz). The resultant solution was then passed through Permutit W anion exchange resin which is an addition polymer having amine type active groupings. The efiluent solution had a pH of 4.72 and contained 50.4 g./l. of NaHPOs and 11.0 g./l. of NaHzPOz. Thus the phosphite content was reduced from 110.8 g./l. to 50.4 g./l.

Example 2 A nickel reduction plating solution containing 70.6 g./ 1. of NazHPOa and 9.0 g./l. of NaHzPOz was treated with sufficient hypophosphorous acid to produce a hypophosphite content of 18.6 g./l. The resultant solution was then passed through Permutit W anion exchange resin. The

eflluent solution contained 32.8 g./l. of NaHPOa and 15.9 g./l. of NaHzPOz. Thus the phosphite content was reduced from 70.6 g./l. to 32.8 g./1.

It will be understood, of course, that the ion exchange resin instead may be treated with hypophosphorous acid, sodium hypophosphite or the like in a separate step, as shown in Reactions 1 and/or 2, prior to passing the plating solution through the resin.

Typical of a nickel reduction plating bath which may be regulated in operation by the practice of the present invention is the following Where the quantities expressed are per liter of water:

Nickel chloride grams 30 Sodium hypophosphite d Glycollic acid (70%) milliliters Sodium hydroxide "grams" 15 It will be understood of course that the above bath composition is intended only as an illustration of a typical reduction plating bath and that the present invention is applicable to a wide range of bath compositions. For example, plating baths containing about 5 to grams per liter of a water-soluble nicket salt such as nickel chloride, nickel acetate, nickel sulfate, etc.; approximately 5 to 100 grams per liter of a reducing agent, such as hypophosphorous acid, sodium hypophosphite, potassium hypophosphite or other soluble hypophosphites; and about 15 to 100 grams per liter of glycollic acid, sodium hydroxy acetate, sodium acetate, sodium citrate, etc. and/ or other bath additives can similarly be treated in accordance with the present invention.

In general, I have found that electroless nickel plat ing baths of the type contemplated herein operate most satisfactorily at a pH within the range of about 3.5 to a pH at which a nickel salt is precipitated, a preferred pH range being from about 5.0 to 5.5. In most instances, an electroless nickel bath is operated most satisfactorily at a temperature of at least about 160 F. although a temperature within the range from approximately 190 F. to 210 F. is preferred. Any chemically resistant material such as stainless steel, glass, ceramic ware, rubber, or plastics such as polyethylene, saran, various phenolic and vinyl resins may be employed in the fabrication of containers for the ion exchange material. Although the temperature at which the ion exchange treatment is conducted may be varied in particular applications, it is generally desirable to employ as low a temperature as possible, preferably about room temperature, in order to avoid possible chemical attack on the ion exchange material.

It is to be understood that, although the invention has been described with specific reference to particular embodiments thereof, it is not to be so limited since changes and alterations therein may be made which are within the full intended scope of this invention as defined by the appended claims.

What is claimed is:

1. In a chemical reduction nickel plating process utilizing a plating bath comprising an aqueous solution containing a water-soluble nickel salt and a hypophosphite reducing agent, the improvement which consists of replenishing the hypophosphite in said bath by addition of hypophosphorous acid and treating said bath with an anion exchange material to remove phosphite ions produced by said process.

2. In the deposition of nickel from a chemical reduction solution, the improvement which consists of removing phosphite ions accumulating in said solution during the plating operation by passing said plating bath through an ion exchange resin which has been treated with a.

source of hypophosphite ions.

3. In the deposition of nickel from a chemical reduction plating solution, the improvement which consists of removing phosphite impurities accumulating in said solution during plating by subjecting said solution to an anion exchange resin which has previously been treated with an alkali and a substance selected from the group consisting of hyphosphorous acid and soluble hypophosphites.

4. A method of purifying an electroless nickel plating solution, said method comprising passing said solution through an ion exchange material which is capable of supplying hypophosphite ions to said bath and removing phosphite ions therefrom without substantial adsorption of weakly acidic bath constituents.

5. A method of treating chemical reduction plating solutions, said method comprising passing said solution through an anion exchange material capable of adsorbing phosphite ions from said solution and adding a hypophosphite reducing agent to said solution.

6. A method as in claim 5 in which the anion exchange material is characterized by at least one active amine grouping.

7. A method as in claim 5 in which the anion exchange material is characterized by at least one active hydroxy grouping.

8. A method of treating contaminated chemical reduction plating solutions to remove accumulated phosphite ions therefrom, said method comprising adding hypophosphorous acid to said solution and thereafter passing the resultant solution through an anion exchange resin.

9. A method of treating contaminated chemical reduction plating solutions to remove therefrom accumulated phosphite ions, said method comprising adding hypophosphorous acid to said solution and thereafter passing the resultant solution through an anion exchange resin, said resin having been previously treated with an alkaline material.

10. In the deposition of nickel from an aqueous chemical reduction plating bath comprising 5 to 30 grams per liter of a water-soluble nickel salt, approximately 5 to grams per liter of a hypophosphite type reducing agent, said bath being operated at a pH of at least 3.5 and at a temperature of at least F., the improvement which consists of replenishing the reducing agent in said bath by addition of hypophosphite ions and removing phosphite ions which gradually accumulate in said bath during the deposition of nickel by treating the bath with an anion exchange material capable of adsorbing phosphite ions.

11. in a chemical reduction nickel plating process utilizing an aqueous solution containing a compound of nickel and a hypophosphite reducing agent, the improvement which consists of treating the solution with an anion exchange material to remove phosphite ions produced during the process.

12. in a chemical reduction plating process utilizing an aqueous solution containing a nickel compound and a hypophosphite reducing agent, the improvement which consists of maintaining the nickel concentration in said solution by addition of soluble nickel compound and treating said solution with an anion exchange material to remove phosphite ions and the anions of the soluble nickel compound to prevent accumulation of said phosphite ions and said anions in said solution.

References Cited in the file of this patent UNITED STATES PATENTS Brenner et a1. Dec. 5, 1950 6 OTHER REFERENCES 5 No. 2, February 1950.

Sussman et aL: Industrial and Engineering Chemistry, vol. 37, No. 7, July 1945. 

1. IN A CHEMICAL REDUCTION NICKEL PLATING PROCESS UTILIZING A PLATING BATH COMPRISING AN AQUEOUS SOLUTION CONTAINING A WATER-SOLUBLE NICKEL SALT ANS A HYPOPHOSPHITE REDUCING AGENT, THE IMPROVEMENT WHICH CONSISTS OF REPLENISHING THE HYPOPHOSPHITE IN SAID BATH BY ADDITION OF HYPOPHOSPHOROUS ACID AND TREATING SAID BATH WITH AN ANION EXCHANGE MATERIAL TO REMOVE PHOSPHITE IONS PRODUCED BY SAID PROCESS. 